Collaborative Research: Interfacial Water Restructuring: An Unrecognized Contribution to Mineral Surface Reactivity

Washington University, Saint Louis MO

Investigators

Abstract

With this award, the Environmental Chemical Sciences Program of the Division of Chemistry is funding Professor Jeffrey G. Catalano of Washington University in St. Louis and Professor Sara E. Mason of the University of Iowa to investigate how the arrangement of water molecules near a mineral surface affects the adsorption of contaminants. Adsorption is a key chemical process at environmental interfaces that directly controls contaminant fate and nutrient availability and is an important precursor step in the nucleation and growth of precipitates, surface-catalyzed redox reactions, and microbial and ligand-promoted dissolution of oxide minerals. While adsorption mechanisms and the effect of surface potential on interfacial reactions are well established, little is known about the role of interfacial water. The information gleaned from these studies is expected to provide insight into fundamental reaction mechanisms involved in important environmental processes such as contaminant fate, transport, and degradation, nutrient bioavailability, carbon dioxide sequestration, and nanoparticle mobilization. This project integrates graduate students, undergraduate students, and high school student interns into the conduct of the research and supports new educational and outreach activities. A graduate student at Washington University will be trained in STEM pedagogies and then develop new active learning activities for a course on the environment and human health. At the University of Iowa, an annual museum exhibit will be prepared to educate K-12 students on the societal importance of geochemical surface science. The objective of this project is to characterize adsorbate-induced interfacial water restructuring on mineral surfaces and its dependence on surface structure, surface charging, and fluid composition. Preliminary data shows that arsenate adsorption on aluminum oxide surfaces alters interfacial water structure. Wholesale restructuring occurred on a surface with weak initial water ordering whereas a small structural perturbation was observed on a surface with strong ordering. Such structural transitions of interfacial water are expected to affect the energetics and kinetics of interfacial reactions. This investigation integrates experimental and computational studies of interfacial water behavior on aluminum and iron oxide surface during arsenate adsorption. More specifically, the work integrates synchrotron-based surface crystallography techniques, laboratory measurements of adsorption isotherms and kinetics, density functional theory calculations, and ab initio molecular dynamics simulations to study how the structure of interfacial water responds to the adsorption of the contaminant arsenic and how such effects vary with mineral surface structure and charging. This study is anticipated to reveal a previously unrecognized mechanism that affects the energetics and kinetics of interfacial reactions.